High hardness metal powder injection molded high strength steel powder

Abstract

The present application relates to high-hardness metal powder injection molding high-strength steel powder, which is mixed by powder A and powder B in a weight ratio of 75-82:18-25; the powder A is composed of the following components in weight percentage: C 0.15-0.3%, Cr 6.0-8.0%, Ni 3.0-5.0%, Co 6.0-10.0%, W 2.0-5.0%, Nb 0.1-1.0%, Si≤0.5%, Mn≤0.5%, S≤0.01%, P≤0.01%, and the balance of Fe and inevitable impurities; the sum of weight percentage of Ni, Co and W is 14%-18%; the weight ratio of Ni to Co is 1:2-2.5. The steel structure member has a tensile strength of 2100-2250 MPa, a yield strength of 1800-1885 MPa, an elongation after fracture of 7.5-8.5%, and a hardness HRC of 55-57.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal powder injection molding, and particularly relates to a high-hardness metal powder injection molding high-strength steel powder. BACKGROUND

[0002] Metal powder injection molding technology (MIM) occupies an important position in modern manufacturing due to its advantage of batch production of complex-shaped parts. In the preparation of high-strength steel parts, the characteristics of the powder (such as chemical composition, particle size distribution) and the molding process parameters directly affect the performance of the final product.

[0003] At present, the commonly used high-strength steel powder in the prior art is designed with a single component, and the component system is difficult to balance the strength, hardness and toughness at the same time. At the same time, the powder with a single particle size distribution is prone to have high porosity and insufficient densification during sintering, resulting in a decrease in the mechanical properties of the parts. The prior art usually increases the content of alloying elements to enhance the strength and corrosion resistance of the steel, but too high content of alloying elements will significantly increase the cost of the material, and the pre-alloyed powder with complex composition and high alloying is prone to element segregation during atomization preparation, and the sphericity and flowability of the powder are difficult to guarantee, resulting in poor powder formability and increasing the difficulty of subsequent MIM process. The use of ultra-fine powder can improve the sintering densification, but the preparation cost of ultra-fine powder is high, and the powder flowability is poor and the green strength is insufficient during injection molding. Therefore, it is a technical problem to be solved in the field to develop a high-strength steel powder with moderate cost, excellent formability, and the ability to simultaneously improve the strength, hardness and toughness of the steel structure. SUMMARY

[0004] The application provides a high-hardness metal powder injection molding high-strength steel powder, which solves the technical problem that the powder with a single component and particle size is difficult to balance the strength, hardness and toughness at the same time and has a high cost. The application designs a double-powder multi-particle size collaborative system, optimizes the powder composition and preparation process, and significantly improves the strength, hardness and toughness of the steel structure, which is suitable for the manufacturing of precise structure parts with high requirements for comprehensive performance of the material. The steel structure prepared from the high-hardness metal powder injection molding high-strength steel powder has excellent mechanical properties, the tensile strength is 2100-2250 MPa, the yield strength is 1800-1885 MPa, the elongation after fracture is 7.5-8.5%, and the hardness HRC is 55-57.

[0005] In the first aspect, the application relates to a high-hardness metal powder injection molding high-strength steel powder, wherein the high-strength steel powder is mixed by powder A and powder B at a weight ratio of 75-82:18-25, the average particle size of the powder A is 10-20 μm, and the average particle size of the powder B is 25-35 μm.

[0006] The powder A is composed of the following components in percentage by weight: C 0.15-0.3%, Cr 6.0-8.0%, Ni 3.0-5.0%, Co 6.0-10.0%, W 2.0-5.0%, Nb 0.1-1.0%, Si≤0.5%, Mn≤0.5%, S≤0.01%, P≤0.01%, and the balance of Fe and inevitable impurities.

[0007] The sum of the weight percentages of Ni, Co and W in the high-strength steel powder A is 14%-18%.

[0008] The weight ratio of Ni to Co is 1:2-2.5.

[0009] The powder B is composed of the following components in percentage by weight: Ni 20-30%, Ti 15-30%, Nb 10-16%, Mo 1.0-3.0%, and the balance of Fe and inevitable impurities.

[0010] Preferably, the weight ratio of the powder A to the powder B in the high-strength steel powder is 80:20.

[0011] Preferably, the raw materials meeting the components of the powder A and the powder B are separately smelted under a protective atmosphere, the alloy melt is atomized by a high-pressure gas atomization method to obtain an initial powder, and the initial powder is finely classified and screened by an air classifier to obtain the powder A and the powder B.

[0012] In a second aspect, the present application relates to a method for preparing a steel structural part by using the high-hardness metal powder injection molding high-strength steel powder, comprising the following steps: S1: mixing the powder A and the powder B in a proportion to form a mixed powder, mixing the mixed powder with a binder to obtain feed particles.

[0013] S2: injection molding the feed particles into a green body under the conditions of an injection temperature of 180-210°C and an injection pressure of 80-140 MPa.

[0014] S3: performing nitric acid catalytic debinding on the green body at 110-130°C to obtain a debound body.

[0015] S4: performing two-stage sintering on the debound body: first stage: performing thermal debinding in a vacuum furnace at 520-550°C at a heating rate of 2-5°C / min; second stage: vacuum sintering at 1300-1350°C at a heating rate of 2-4°C / min, holding for 60-180 min, and cooling to room temperature to obtain a sintered body.

[0016] S5: sequentially subjecting the sintered body to solid solution treatment and aging treatment to obtain the steel structural part.

[0017] Preferably, the binder is composed of 60-70 parts of polypropylene, 4-8 parts of high-density polyethylene, 1-2 parts of stearic acid and 20-25 parts of paraffin wax, and the binder accounts for 8-10% of the mass fraction of the feed granules.

[0018] Preferably, the amount of nitric acid introduced in step S3 is 3.5-4.5 ml / min, and the degreasing treatment is performed for 1-2 h.

[0019] Preferably, the solid solution treatment in step S5 is performed at 800-1000 DEG C for 1-1.5 h, followed by water cooling to room temperature, and the aging treatment is performed at 350-400 DEG C for 2-3 h.

[0020] The present application has the advantages that two powders with different particle size distributions are used, i.e., fine powder A (10-20 μm) and coarse powder B (25-35 μm), and in the mixing process, a high-efficiency bimodal particle size distribution is formed, which significantly improves the tap density of the mixed powder and the green density of the subsequent feed. The combination of the two powders reduces the alloy manufacturing cost, has better formability than the existing single-component or single-particle-size powder, and the mechanical properties of the two powders complement each other, thereby improving the tensile strength and yield strength, elongation and hardness of the steel.

[0021] By optimizing the addition amount of Ni, Co and W in powder A and adjusting the ratio of the three elements, the synergistic strengthening effect of the three elements is achieved. The total amount of the three elements is controlled in the range of 14%-18%, and the weight ratio of Ni to Co is controlled in the range of 1:2-2.5, which can ensure the strength and hardness of the material while avoiding the decrease in toughness and the increase in cost caused by excessive alloy elements, and is a key means for realizing excellent comprehensive performance of strength, toughness and hardness.

[0022] The steel structure prepared by the high-hardness metal powder injection molding high-strength steel powder has excellent mechanical properties, the tensile strength is 2100-2250 MPa, the yield strength is 1800-1885 MPa, the elongation after fracture is 7.5-8.5%, and the hardness HRC is 55-57. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0024] Figure 1 The present application discloses a method for preparing a steel structure by high-hardness metal powder injection molding high-strength steel powder. DETAILED DESCRIPTION

[0025] The technical solutions of the present application will be described clearly and completely below in conjunction with the drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0026] At present, the existing high-strength steel powder is designed by using a single component, and the component system is difficult to balance the strength, hardness and toughness at the same time. Meanwhile, the powder with a single particle size distribution is prone to have high porosity and insufficient densification in the sintering process, resulting in the decline of the mechanical properties of the parts.

[0027] In view of the above technical problems, the present application provides a high-hardness metal powder injection molding high-strength steel powder, wherein the high-strength steel powder is mixed by powder A and powder B in a weight ratio of 75-82:18-25, the average particle size of the powder A is 10-20 μm, and the average particle size of the powder B is 25-35 μm; wherein the powder A is composed of the following components in a weight percentage: C 0.15-0.3%, Cr 6.0-8.0%, Ni 3.0-5.0%, Co 6.0-10.0%, W 2.0-5.0%, Nb 0.1-1.0%, Si≤0.5%, Mn≤0.5%, S≤0.01%, P≤0.01%, and the balance is Fe and inevitable impurities; in the high-strength steel powder A, the sum of the weight percentages of Ni, Co and W is 14%-18%, and the weight ratio of Ni to Co is 1:2-2.5; the powder B is composed of the following components in a weight percentage: Ni 20-30%, Ti 15-30%, Nb 10-16%, Mo 1.0-3.0%, and the balance is Fe and inevitable impurities.

[0028] In one embodiment, the weight ratio of the powder A to the powder B in the high-strength steel powder is 80:20.

[0029] In one embodiment, the raw materials meeting the components of the powder A and the powder B are respectively smelted under a protective atmosphere, the high-pressure gas atomization method is used to atomize the alloy melt to obtain an initial powder, and the airflow classifier is used to finely classify and screen the initial powder to obtain the powder A and the powder B.

[0030] The high-strength steel powder is mixed by powder A and powder B in a weight ratio of 75-82:18-25. Powder A serves as the matrix phase, providing a good foundation for mechanical properties. Powder B is a pre-alloyed powder rich in strong precipitation strengthening elements. During high-temperature sintering, the high concentration of alloying elements in powder B will diffuse and react with the surrounding powder A matrix, providing core elements for the formation of nanoscale strengthening phases in the final heat treatment step. By mixing two powders with optimized performance and particle size, more precise microstructure control is achieved than traditional master alloy methods. When the proportion of powder A is less than 75%, the matrix phase is insufficient to ensure the basic toughness of the material; when the proportion of powder A is higher than 82%, the strengthening phase is too small to have a significant strengthening effect. The preferred ratio is 80:20, at which the matrix phase and strengthening phase can achieve the best synergistic effect, and the overall performance of the material is optimal.

[0031] The average particle size of powder A is 10-20 μm, and the average particle size of powder B is 25-35 μm. The particle size range takes into account the flowability and sintering activity of the powder. Smaller particle sizes are beneficial for improving sintering densification, but too small particle sizes can lead to poor powder flowability, which is not conducive to injection molding. Larger particle sizes can improve flowability, but can reduce sintering activity, leading to increased porosity. The particle sizes of powder A and powder B form a complementary particle size, and the dual-particle-size synergistic effect improves the packing density of the powder. The particle size of powder B is larger than that of powder A, which can fill the gaps between powder A particles, reduce porosity during sintering, and improve densification.

[0032] Powder A is composed of the following components by weight percentage: C 0.15-0.3%, Cr 6.0-8.0%, Ni 3.0-5.0%, Co 6.0-10.0%, W 2.0-5.0%, Nb 0.1-1.0%, Si≤0.5%, Mn≤0.5%, S≤0.01%, P≤0.01%, and the balance being Fe and unavoidable impurities.

[0033] The content of C is 0.15-0.3%: Carbon is an important element for strengthening steel, which can form carbides to increase the hardness and strength of steel. If the content is less than 0.15%, the strengthening effect is insufficient; if it is higher than 0.3%, the toughness of the steel will decrease, and net-shaped carbides will form, reducing the plasticity of the material.

[0034] The content of Cr is 6.0-8.0%: Chromium can improve the corrosion resistance and oxidation resistance of steel, and also helps to form stable carbides. Cr is also a carbide-forming element that helps secondary hardening and significantly improves the hardenability of steel. If the content is less than 6.0%, the corrosion resistance will not be significantly improved; if it is higher than 8.0%, the production cost of the powder will increase, and the brittleness of the steel may also increase.

[0035] Ni: 3.0-5.0%: Ni is an important austenite stabilizing element, which can expand the austenite phase region and reduce the martensite transformation point, thereby improving the hardenability of the steel. Ni can also significantly improve the low temperature toughness of the steel and increase the corrosion resistance of the steel. In combination with Co and W, the strength of the material can be further improved. If the content is too low, the toughness improvement effect is not good, and if it is too high, the cost will increase.

[0036] Co: 6.0-10.0%: Co is an important strengthening element that promotes the formation of precipitates. With the increase of Co content, the precipitates in the aged martensitic steel will be more dispersedly distributed, which can effectively enhance the precipitation strengthening effect of the precipitates. Smaller and more dispersed precipitates can make the material have higher toughness and strength. Cobalt cooperates with Ni and W to form solid solution strengthening and improve the overall mechanical properties of the material. If the content is less than 6.0%, the strengthening effect is not enough, and if it is higher than 10.0%, the material will become more brittle.

[0037] W: 2.0-5.0%: Tungsten can form hard carbides, significantly improve the hardness and wear resistance of the steel, and improve the high temperature strength of the steel. If the content is too low, the strengthening effect is not obvious, and if it is too high, the preparation difficulty of the powder will increase, and the toughness of the steel may decrease.

[0038] Nb: 0.1-1.0%: Niobium can refine the grain and inhibit the growth of austenite grains, thereby improving the strength and toughness of the steel. At the same time, the carbide stability of niobium is high, which can improve the high temperature performance of the steel. If the content is less than 0.1%, the refining effect is not obvious, and if it is higher than 1.0%, coarse carbides may be formed, which will affect the performance of the material.

[0039] Si≤0.5%, Mn≤0.5%: Silicon and manganese are added as deoxidizers to remove oxygen in the steel and improve the purity of the steel. However, too high a content will increase the brittleness of the steel, so it needs to be controlled at a low level.

[0040] S≤0.01%, P≤0.01%: Sulfur and phosphorus are harmful elements in steel, which can reduce the toughness and welding performance of the steel, so their content needs to be strictly controlled at a very low level.

[0041] The sum of the weight percentages of Ni, Co and W in the powder A is 14% to 18%, and the weight ratio of Ni to Co is 1:2 to 2.5. This design is to realize the synergistic effect of the three elements. Ni mainly improves the toughness and basic solid solution strengthening; Co provides strong solid solution strengthening and promotes secondary hardening, W mainly improves the hardness and wear resistance, the total amount of the three is controlled in the range of 14% to 18%, and the weight ratio of Ni to Co is controlled in the range of 1:2 to 2.5, so that the toughness is prevented from being reduced and the cost is prevented from being increased due to too many alloying elements while the strength and hardness of the material are ensured, which is a key means for realizing the excellent comprehensive performance of strength, toughness and hardness.

[0042] The powder B is composed of the following components with the weight percentages: Ni 20% to 30%, Ti 15% to 30%, Nb 10% to 16%, Mo 1.0% to 3.0%, and the balance of Fe and inevitable impurities.

[0043] The content of Ni is 20% to 30%, and the content of Ti is 15% to 30%. These two elements are the basis for forming the famous high-strength intermetallic compound γ' phase. In the subsequent aging process, the Ni and Ti precipitated from the matrix will form in situ a dispersed, fine and coherent or semi-coherent γ' phase, which can extremely effectively hinder dislocation movement and produce excellent precipitation strengthening effect. High content of nickel can improve the toughness of the overall material after mixing with the powder A, and at the same time form alloy phases with other elements to improve the strengthening effect.

[0044] The content of Nb is 10% to 16%. In the powder B, niobium mainly forms complex intermetallic compounds with titanium, nickel and other elements, further enhances the dispersion strengthening effect, refines the grains and improves the strength and toughness of the material.

[0045] The content of Mo is 1.0% to 3.0%. Mo can produce a secondary hardening effect in the aging process and can solid solution strengthen the matrix to improve the overall strength of the material, and at the same time improve the corrosion resistance of the material.

[0046] As shown in Figure 1 A method for preparing a steel structural part by using the high-hardness metal powder injection molding high-strength steel powder according to the embodiment of the present application, comprising the following steps: S1: mixing the powder A and the powder B in a proportion to form a mixed powder, mixing the mixed powder with a binder to obtain feed particles.

[0047] S2: injection molding the feed particles into a green body under the conditions of an injection temperature of 180 to 210℃ and an injection pressure of 80 to 140MPa.

[0048] S3: performing nitric acid catalytic debinding on the green body at 110 to 130℃ to obtain a debound body.

[0049] S4: the defatted blank is subjected to two-stage sintering: first stage: thermal debinding at 520-550℃ in a vacuum furnace, heating rate 2-5℃ / min; second stage: vacuum sintering at 1300-1350℃, heating rate 2-4℃ / min, holding for 60-180min, cooling to room temperature to obtain a sintered blank.

[0050] S5: the sintered blank is subjected to solid solution treatment and aging treatment to obtain the steel structural part.

[0051] In one embodiment, the binder is composed of 60-70% polypropylene, 4-8% high-density polyethylene, 1-2% stearic acid, and 20-25% paraffin wax, and the binder accounts for 8-10% of the mass fraction of the feed particles.

[0052] In one embodiment, the amount of nitric acid introduced in step S3 is 3.5-4.5ml / min, and the debinding treatment is performed for 1-2h.

[0053] In one embodiment, the solid solution treatment in step S5 is performed at 800-1000℃ for 1-1.5h and then water-cooled to room temperature, and the aging treatment is performed at 350-400℃ for 2-3h.

[0054] The binder is composed of 60-70 parts of polypropylene, 4-8 parts of high-density polyethylene, 1-2 parts of stearic acid, and 20-25 parts of paraffin wax, and the binder accounts for 8-10% of the mass fraction of the feed particles. Polypropylene serves as the main component of the binder, providing the strength and flowability of the feed, and its content is 60-70 parts, which can ensure that the feed has sufficient plasticity and stability during injection molding. High-density polyethylene: helps to improve the strength and toughness of the feed, and its content is 4-8 parts, which synergistically acts with polypropylene to improve the molding performance of the feed. Stearic acid: as a lubricant, it can reduce the friction between the feed particles and improve the flowability of the feed, and its content is 1-2%, and excessive content will lead to a decrease in the strength of the feed. Paraffin wax: has good plasticity and flowability, and can improve the injection molding performance of the feed, and its content is 20-25 parts, and insufficient content will result in insufficient flowability of the feed, and excessive content will affect the debinding effect.

[0055] Step S4: The debound green body is sintered in two stages. First stage: thermal debinding at 520-550℃ in a vacuum furnace with a heating rate of 2-5℃ / min. This stage is mainly to remove the residual binder, and the vacuum environment can prevent the green body from being oxidized. Second stage: vacuum sintering at 1300-1350℃ with a heating rate of 2-4℃ / min, holding for 60-180min, and cooling to room temperature to obtain the sintered body. The dual-particle-size system exhibits unique kinetic advantages during sintering. In the early stage of sintering, fine powder A with larger specific surface area and higher sintering activity will start to neck and migrate first, forming a preliminary sintering skeleton connecting coarse powder B. As the temperature further rises, this skeleton provides structural support for the entire system and becomes a channel for atomic diffusion, accelerating the dissolution, diffusion of coarse powder B, and the densification process of the entire system. Compared with single-particle-size powder, the dual-particle-size system can achieve higher density at lower sintering temperature or in shorter time.

[0056] Step S5: The sintered body is subjected to solid solution treatment and aging treatment to obtain the steel structural part.

[0057] Solid solution treatment: water cooling to room temperature after holding at 800-1000℃ for 1-1.5h. Solid solution treatment can make alloying elements fully dissolve into the matrix to form a uniform solid solution, preparing for subsequent aging treatment to precipitate strengthening phases. The temperature range of 800-1000℃ can ensure the full dissolution of alloying elements, holding for 1-1.5h can make the dissolution process complete, and water cooling can quickly inhibit the precipitation of alloying elements, maintaining the supersaturated state of the solid solution. Aging treatment: holding at 350-400℃ for 2-3h. Aging treatment can make alloying elements in the supersaturated solid solution precipitate to form fine strengthening phases, which can hinder dislocation movement, significantly improving the strength and hardness of the material.

[0058] The following describes an embodiment of the present application, which uses a high-hardness metal powder injection molding high-strength steel powder as follows: the high-strength steel powder is mixed from powder A and powder B in a weight ratio of 75-82:18-25, the powder A has an average particle size of 10-20 μm; the powder B has an average particle size of 25-35 μm; wherein the powder A is composed of the following components in weight percentage: C 0.15-0.3%, Cr 6.0-8.0%, Ni 3.0-5.0%, Co 6.0-10.0%, W 2.0-5.0%, Nb 0.1-1.0%, Si≤0.5%, Mn≤0.5%, S≤0.01%, P≤0.01%, and the balance being Fe and inevitable impurities; in the high-strength steel powder A, the sum of the weight percentages of Ni, Co, and W is 14%-18%; the weight ratio of Ni to Co is 1:2-2.5; the powder B is composed of the following components in weight percentage: Ni 20-30%, Ti 15-30%, Nb 10-16%, Mo 1.0-3.0%, and the balance being Fe and inevitable impurities.

[0059] The raw materials meeting the components of the powder A and the powder B are separately smelted under a protective atmosphere; the alloy melt is atomized by using a high-pressure gas atomization method to obtain an initial powder; the initial powder is finely classified and screened by using an air flow classifier to obtain the powder A and the powder B.

[0060] The embodiment uses the high-hardness metal powder injection molding high-strength steel powder to prepare a steel structural member, which includes the following steps: S1: mixing the powder A and the powder B in a proportion to form a mixed powder, mixing the mixed powder with a binder to obtain feed particles.

[0061] S2: injection molding the feed particles into a green body under the conditions of an injection temperature of 180-210 ℃ and an injection pressure of 80-140 MPa.

[0062] S3: performing nitric acid catalytic debinding on the green body at 110-130 ℃ to obtain a debound body.

[0063] S4: performing two-stage sintering on the debound body: first stage: performing thermal debinding at 520-550 ℃ in a vacuum furnace at a heating rate of 2-5 ℃ / min; second stage: vacuum sintering at 1300-1350 ℃ at a heating rate of 2-4 ℃ / min, holding for 60-180 min, and cooling to room temperature to obtain a sintered body.

[0064] S5: sequentially subjecting the sintered body to solid solution treatment and aging treatment to obtain the steel structural member.

[0065] The binder is composed of 60-70 parts of polypropylene, 4-8 parts of high density polyethylene, 1-2 parts of stearic acid and 20-25 parts of paraffin wax in mass fraction, and the binder accounts for 8-10% of the mass fraction of the feed particles.

[0066] The amount of nitric acid in the step S3 is 3.5-4.5 ml / min, and the degreasing treatment is 1-2 h.

[0067] The solid solution treatment in the step S5 is water-cooled to room temperature after being kept at 800-1000 ℃ for 1-1.5 h, and the aging treatment is kept at 350-400 ℃ for 2-3 h.

[0068] The high-hardness metal powder injection-molded high-strength steel powder composition of the examples 1-4 and the comparative examples 1-5 is shown in Table 1.

[0069] Table 1: High-strength steel powder A composition of the examples 1-4 and the comparative examples 1-5:

[0070]

[0071] Note: The component content in Table 1 is mass percentage.

[0072] Table 2: High-strength steel powder composition of the examples 1-4 and the comparative examples 1-5:

[0073]

[0074] Note: The component content of powder B is weight percentage.

[0075] The process parameters of the steel structure preparation method of the examples 1-4 and the comparative examples 6-8 using the high-hardness metal powder injection-molded high-strength steel powder are shown in Table 3.

[0076] Table 3: Process parameters of the steel structure preparation method of the examples 1-4 and the comparative examples 6-8:

[0077]

[0078] The process parameters of the steel structure preparation method of the comparative examples 1-5 using the high-hardness metal powder injection-molded high-strength steel powder are the same as those of the example 3, and are shown in Table 3.

[0079] The high-hardness metal powder injection-molded high-strength steel powder composition of the comparative examples 6-8 is the same as that of the example 4, and the preparation process parameters are shown in Tables 1 and 2.

[0080] The tensile strength, yield strength, elongation after fracture, hardness performance of the steel structure prepared by the examples and the comparative examples are measured, and the results are shown in Table 4.

[0081] Table 4: Performance data of examples and comparative examples

[0082]

[0083] From Table 4, it can be found that the steel structural parts prepared from the high-hardness metal powder injection-molded high-strength steel powder have excellent mechanical properties, the tensile strength is 2180-2250 MPa, the yield strength is 1830-1885 MPa, the elongation after fracture is 7.8-8.2%, and the hardness HRC is 55-57.

[0084] Compared with Example 3, the coordination of each component in the powder is weakened, and the particle size matching between the powders cannot fully play a role after adjusting the components of the high-hardness metal powder injection-molded high-strength steel powder and the particle size and ratio of the powder A and the powder B in Comparative Examples 1-5, resulting in a significant decrease in the tensile strength, the yield strength, the elongation after fracture, and the hardness.

[0085] Compared with Example 4, it is difficult to ensure the mechanical properties of the steel structural parts after adjusting the preparation process of the steel structural parts, without performing heat defatting, adjusting the composition of the binder, and adjusting the sintering process in Comparative Examples 6-8, resulting in a significant decrease in the tensile strength, the yield strength, the elongation after fracture, and the hardness.

[0086] The technical features of the above-described examples can be combined arbitrarily, and for the sake of brevity, all possible combinations of the technical features in the above-described examples are not described, however, as long as the combinations of the technical features do not contradict, they should be considered as the scope of the present disclosure.

Claims

1. A high-hardness metal powder injection molded high-strength steel powder, characterized by, The high-strength steel powder is mixed by powder A and powder B in a weight ratio of 75-82:18-25, the average particle size of the powder A is 10-20μm; the average particle size of the powder B is 25-35μm; The powder A is composed of the following components in weight percentage: C 0.15-0.3%, Cr 6.0-8.0%, Ni 3.0-5.0%, Co 6.0-10.0%, W 2.0-5.0%, Nb 0.1-1.0%, Si≤0.5%, Mn≤0.5%, S≤0.01%, P≤0.01%, and the balance of Fe and inevitable impurities; In the high-strength steel powder A, the sum of the weight percentage of Ni, Co and W is 14%-18%; The weight ratio of Ni to Co is 1:2-2.5; The powder B is composed of the following components in weight percentage: Ni 20-30%, Ti 15-30%, Nb 10-16%, Mo 1.0-3.0%, and the balance of Fe and inevitable impurities.

2. The high hardness metal powder for powder injection molding of high strength steel according to claim 1, wherein, The weight ratio of powder A to powder B in the high-strength steel powder is 80:

20.

3. The high hardness metal powder for powder injection molding of high strength steel according to claim 1, wherein, The raw materials meeting the components of the powder A and powder B are respectively smelted under a protective atmosphere; the alloy melt is atomized by a high-pressure gas atomization method to obtain an initial powder; the initial powder is finely classified and screened by an air flow classifier to obtain the powder A and the powder B.

4. A method for producing a steel structural part using the high-hardness metal powder injection-molded high-strength steel powder according to any one of claims 1 to 3, characterized by, The method comprises the following steps: S1: mixing the powder A and powder B in a proportion to form a mixed powder, mixing the mixed powder with a binder to obtain feed particles; The binder is composed of polypropylene 60-70 parts, high-density polyethylene 4-8 parts, stearic acid 1-2 parts, and paraffin 20-25 parts in mass fraction, and the binder accounts for 8-10% of the mass fraction of the feed particles; S2: injection molding the feed particles into a green body under the conditions of an injection temperature of 180-210℃ and an injection pressure of 80-140MPa; S3: nitric acid catalytic debinding the green body at 110-130℃ to obtain a debound body; S4: two-stage sintering the debound body: First stage: thermal debinding at 520-550℃ in a vacuum furnace at a heating rate of 2-5℃ / min; second stage: vacuum sintering at 1300-1350℃ at a heating rate of 2-4℃ / min, holding for 60-180min, and cooling to room temperature to obtain a sintered body; S5: sequentially subjecting the sintered body to solid solution treatment and aging treatment to obtain the steel structural part.

5. The method of producing a steel structural member according to claim 4, characterized by, In the step S3, the amount of nitric acid introduced is 3.5-4.5ml / min, and the debinding treatment is performed for 1-2h.

6. The method of claim 4, wherein the steel structural member is a steel pipe. In the step S5, the solid solution treatment is performed at 800-1000℃ for 1-1.5h and then water-cooled to room temperature, and the aging treatment is performed at 350-400℃ for 2-3h.

Images